Commercially-available formats for nucleic acid purification include spin columns, magnetic beads in a tube or the use of vacuum to draw liquids through a column or plate. In these formats, nucleic acids are isolated as follows. The cells are grown in a suitable medium, the culture is centrifuged to collect the cells and the growth medium is discarded. Next, the cells are lysed, e.g., with an alkali solution followed by the addition of a neutralizing solution. Traditionally, a second centrifugation step is performed after lysis to pellet the cell debris and the nucleic acids are purified from the supernatant.
When the spin column format is employed, several additional centrifugations are performed. Because all these methods require at least two centrifugation steps, they are time-consuming, laborious and difficult to fully automate. They require significant human intervention and cannot be performed in a walk-away fashion. Methods involving removal of the particulate from the cell lysate by filtration are not reliable. There exists a need for automated, high-throughput nucleic acid purification in a pipette tip column format. Furthermore, there exists a need for purifying plasmids from unclarified cell lysates and other samples containing particulates and cell debris.